1. Field of the Invention
This invention concerns a process for producing phenols, and in particular to a new synthesis in which a nonaromatic hydrocarbon is reacted with water in the presence of a metal oxide catalyst.
2. Prior Art
Processes for producing phenol are known. L. F. and M. Fieser, "Advanced Organic Chemistry", Rheinhold Publishing Corp., New York, pages 745.747 (1961) describes several such processes including: (a) sulfonation of benzene, followed by alkali fusion; (b) nitration of benzene, reduction to aniline, formation of a diazonium salt, and finally hydrolysis; (c) formation of an aryl halide, followed by alkali hydrolysis; (d) formation of a hydroaromatic ketone, such as cyclohexanone by oxidation of cyclohexane, followed by dehydrogenation; and (e) oxidation of cumene to a hydroperoxide, followed by acid catalysis. Each of these processes suffers from one disadvantage or another.
U.S. Pat. No. 3,180,877 to Benichou et al. describes the catalyst oxidation of a hydrocarbon wherein a nonexplosive mixture of a hydrocarbon and air is heated to about 410.degree. C in the presence of a catalyst to produce an oxygenated compound. The nonexplosive mixture is needed to avoid complete oxidation of the hydrocarbon to water, carbon monoxide and carbon dioxide, as would occur in the uncontrollable reaction engendered by an explosion, and such nonexplosive mixture is obtained by using a large excess of air. In the sole disclosed example, naphthalene and a very large excess of air (e.g., an eight-fold excess of oxygen compared to stoichiometric requirements) are passed through a series of catalyst beds composed of 8% vanadium oxide (V.sub.2 O.sub.5) on an inert carrier to produce phthalic anhydride. The inlet and outlet temperature of each bed is 350.degree. and 410.degree. C, respectively. Cooling is provided by injection of water between successive stages to absorb the heat developed by the highly exothermic reaction, the "water being used because of its high heat of evaporation and of its substantial neutrality to the reaction in progress." The patent suggests that the process can be used to convert cyclohexane to phenol. Contrary to this suggestion, however, it has been found that the reaction of cyclohexane with large excess quantities of air in the presence of water and V.sub.2 O.sub.5 catalyst on an inert carrier does not yield measurable quantities of phenol at temperatures of 350.degree., 400.degree. or at 500.degree. C.